As the costs of energy sources such as oil increase, increasing emphasis in architectural design has been placed on the reduction of heat flow between the inside and outside of buildings. This is particularly true with respect to the casings for glass windows and glass doors.
For example, a popular conventional technique is to make a window sash (the part that contains the glass) from architectural components which each have separate spaced aluminum side portions rigidly connected to each other by a thermal barrier material such as a polyurethane polymer resin. The aluminum side portions provide strength and rigidity, while the thermal barrier material substantially avoids a transfer of heat between the side portions. A very common method of making such a component is to initially extrude a single integral piece of aluminum which includes not only the side portions but also a bridge portion extending between the side portions in order to rigidly interconnect them. A liquid thermal barrier material is then poured into an upwardly open channel defined in part by the bridge portion, after which the thermal barrier material is cured until it is hard and rigidly interconnects the first and second portions. The thermal barrier material typically tends to adhesively bond to the aluminum extrusion as it cures. Then, a conventional milling tool is used to mill away the material of the bridge portion so that the first and second portions literally become two separate parts which are rigidly interconnected only by the thermal barrier material. In other words, a single elongate slot extending the full length of the component is milled into the bridge portion. This technique is disclosed, for example, in Gordon U.S. Pat. No. 4,463,540, the disclosure of which is hereby incorporated herein by reference.
While the architectural component resulting from this approach has been generally adequate for its intended purposes, it has not been satisfactory in all respects. One particular problem relates to resistance to shear stresses, in that the two spaced aluminum portions are held against lengthwise sliding with respect to each other primarily by the adhesive bond which is present between each and the thermal barrier material. The strength of this bond can vary widely from component to component, and in a production situation it has proved difficult to reliably and consistently achieve bond strengths within acceptable limits. One conventional technique for dealing with this problem is known as "skip debridging". In particular, instead of milling into the bridging portion a single slot which extends the full length of the extrusion, several spaced slots which extend along a common lengthwise line are milled into the bridging portion. The adjacent ends of each adjacent pair of slots are spaced from each other by a distance which is approximately one tenth to one twentieth of the overall length of each slot. Thus, in the region between the adjacent ends of adjacent slots, a section of the bridging portion is left to extend between the side portions of the extrusion so as to serve as a connecting portion.
Since this technique leaves small integral aluminum connecting portions extending between the side portions of the extrusion at spaced locations along the length of the extrusion, the connecting portions rigidly and reliably resist any relative lengthwise movement of the side portions, independently of the strength of the adhesive bonds between the thermal barrier material in each side portion. However, a disadvantage is that the aluminum connecting portions which extend between the side portions allow an undesirably large degree of thermal energy transfer between the side portions.
Thus, milling a single slot in the bridging portion along the full length of the extrusion provides excellent thermal separation but unpredictable strength against shear forces, whereas providing periodic interruptions in the slot provide a reliable resistance to shear forces but significantly degrades the thermal separation.
Therefore, an important object of the present invention is therefore to provide an improvement in debridging which assures a high degree of thermal separation while simultaneously providing a reliable high degree of resistance to shear forces.
A further object is to provide such an improvement in debridging which does not increase the complexity or cost of the resulting architectural component, and which does not significantly increase the cost or complexity of the process for manufacturing the component.